The present invention relates to improvements in pierce and clinch nut installation heads of the type disclosed in U.S. Pat. No. 3,089,360 of Multifastener Corporation, the predecessor in interest of the assignee of this application. As disclosed in U.S. Pat. No. 3,089,360, the disclosure which is incorporated herein by reference, pierce and clinch nut installation heads, are typically attached to the upper die shoe or platen of a die press and the installation head simultaneously feeds the pierce or clinch nuts, either in strip or bulk form, to a plunger and installs a pierce or clinch nut through the plunger passage into a metal panel and a die button located in the opposite die shoe or platen permanently installs the nut in the panel. As will be understood by those skilled in this art, the installation head may alternatively be installed in the lower die shoe and the die button may be in the upper die shoe.
A conventional pierce nut installation head, as disclosed in U.S. Pat. No. 3,089,360, for example, includes a base portion, which is generally attached to the upper die shoe, a shank or guidepost, which extends generally perpendicular to the upper die shoe, and a plunger fixed to the base and therefore extends from the upper die shoe. The pierce nut installation head generally further includes a nose member having a plunger passage and a transverse feed passage which receives pierce or clinch nuts for installation in a panel. The nuts are fed to the plunger passage by a feed mechanism and installed by the plunger with each stroke of the die press.
Although the pierce nut installation head disclosed in the above-referenced U.S. patent has been used successfully to install pierce nuts for many years, it would be desirable to simplify the design to reduce the required number of parts and thereby reduce cost, reduce the required size of the pierce nut installation head to increase the number of applications where the pierce nut head may be utilized, improve the feed system by providing a spring-biased pawl which feeds the xe2x80x9cfirst nutxe2x80x9d adjacent the plunger passage to the plunger passage to reduce feeding error and provide a pierce nut installation head which may be utilized to feed and install various types of pierce nuts having common elements or components. These and other advantages are provided by the pierce nut installation head of this invention.
Various attempts have been made to solve the problems associated with the pierce nut installation head described in the above-referenced U.S. patent. For example, a xe2x80x9cpositive feedxe2x80x9d pierce nut installation head is disclosed in U.S. Pat. No. 3,961,408, also assigned to Multifastener Corporation, wherein the feed pawl engages the bore of the pierce nut adjacent the plunger passage during feeding. However, the pierce nut installation head disclosed in this patent was withdrawn by Multifastener Corporation because of problems associated with the positive feed system disclosed in this patent as described below. Thus, it would be desirable to utilize a feed pawl in a pierce nut installation head, wherein the pawl is spring biased to feed the pierce nuts to the plunger passage as the die press is opened as disclosed in the above-referenced U.S. Pat. No. 3,089,360, but wherein the pawl feeds the nut adjacent the plunger passage as described.
Further, U.S. Pat. Nos. 5,636,426, 5,953,813 and 6,263,561 disclose various improvements in retaining the pierce nuts in the plunger passage during movement of the pierce nut through the plunger passage. It would also be desirable to improve the fastener retaining mechanism disclosed in these patents.
The present invention relates to an installation apparatus for installing self-attaching fasteners, particularly including pierce and clinch nuts, a feed mechanism for an installation head for feeding self-attaching fasteners interconnected by a frangible connector, and a method of installing a self-attaching fastener in a panel, wherein the feed mechanism includes a spring-biased feed pawl which feeds the first self-attaching fastener in the feed passage adjacent the plunger passage upon opening of the die press, thereby avoiding problems associated with the installation heads presently on the market. As set forth above, the installation apparatus of this invention includes a base member, which is conventionally attached to the upper shoe of a die press, having a plunger fixed relative to the base member and extending from the base member, a nose member spaced from the base member by a biasing element, such as a spring or pneumatic cylinder, wherein the nose member includes a feed passage and a plunger passage which receives the free end of the plunger, and a feed mechanism which feeds self-attaching fasteners through the feed passage into the plunger passage for installation in a panel located opposite the plunger passage.
The feed mechanism of this invention is particularly, but not exclusively adapted to feed self-attaching fasteners interconnected by a frangible connector, such as disclosed in the above-referenced U.S. Pat. No. 3,845,860. The feed mechanism of this invention includes at least one spring biased feed pawl having an end portion which engages the self-attaching fastener or nut in the feed passage adjacent the plunger passage, which is sometimes referred to herein as the xe2x80x9cfirst fastenerxe2x80x9d or the xe2x80x9cfirst nut,xe2x80x9d but which is actually the last nut in the feed passage, and drives the first fastener adjacent the plunger passage into the plunger passage for installation by the plunger upon opening of the die press. The feed mechanism and method of installation of this invention eliminates several problems associated with the prior installation apparatus. First, the feeding of the first nut in the feed passage adjacent the plunger passage eliminates the problem of misfeeding the self-attaching nuts due to tolerance buildup, particularly where the fasteners are interconnected by a frangible connector element. The fastener installation head disclosed in U.S. Pat. No. 3,942,235, etc. attempted to solve this problem by feeding the first nut in the feed passage adjacent the plunger passage. However, the fastener installation head disclosed in these patents was not successful because the feed pawl was connected to the base member by a linkage, wherein the feed pawl was positively actuated by the linkage upon closing of the die press resulting in breakage of the linkage due to tolerance variations, such that the travel of the feed pawl was not properly controlled.
The preferred embodiment of the feed mechanism of this invention includes a bracket or slide which is movable toward and away from the plunger passage and a feed pawl is pivotally supported on the bracket. A spring biases the bracket toward the plunger passage and a roller is rotatably supported on the bracket opposite an inclined cam surface on the base member. Thus, upon closing of the die press, the roller engages the cam surface, moving the bracket away from the plunger passage. Then, upon opening of the die press, the bracket is urged by the spring toward the plunger passage and the feed pawl then feeds the first nut adjacent the plunger passage into the plunger passage for installation during the next stroke of the press. In the most preferred embodiment, the feed pawl is L-shaped including a first leg portion extending into the feed passage and a second generally transverse leg. A second spring is biased against the transverse leg of the feed pawl, rotating the feed pawl to engage the first nut adjacent the plunger passage. The bracket or slide includes a base portion slidably supported in the feed passage and a transverse bracket portion, and the roller is rotatably supported on the bracket portion of the slide.
In the disclosed embodiment of the feed mechanism of this invention, the feed pawl includes a finger adapted to be received in the nut bore of the first nut in the feed passage adjacent the plunger passage. Where only one nut remains in the feed passage, the end of the feed pawl engages the side of the last nut. However, the feed mechanism of this invention may also be utilized to feed a fastener strip having notches or projections on the exposed sides of the fasteners in the fastener strip as disclosed in a co-pending application assigned to the assignee of this application, wherein two feed pawls are pivotally supported on the slide bracket, thereby eliminating contact with the feed bore and also permitting feeding of fastener elements which do not have a bore or where it is not practical to feed the bore of the fastener. Further, where the feed system of this invention includes two feed pawls which engage notches or projections on the sides of the fasteners, it is possible to use a spring having a greater force which would otherwise damage the nut bore assuring feeding of the fasteners and permitting engagement of a fastener adjacent the plunger passage, but spaced from the plunger passage one or two fasteners thus reducing the likelihood of feed error.
Other problems associated with the present fastener installation heads of the type disclosed herein relate primarily to maintenance. One problem, for example, relates to disassembly of the pierce nut installation head. During service of the head, the nose member must be disassembled from the base member. This is a difficult task with the present fastener installation heads. However, in the fastener installation head of this invention, the nose member is attached to the base member by a shank and the shank is attached to the nose member by removable pins. In the most preferred embodiment, the free end of the shank is rectangular and the nose member includes a rectangular opening which receives the free end of the shank, and the nose member is then retained to the shank by removable pins received through the rectangular free end portion of the shank.
Another problem relates to removal of a nut strip from the installation head such as disclosed in the above-referenced U.S. Pat. No. 3,845,860. As will be understood by those skilled in this art, the pierce nuts may be fed to the feed passage from a spool of nuts and the spool of nuts must be changed periodically by the die press operator. Thus, it would be convenient to be able to remove a small portion of a strip of nuts from the head prior to complete exhaustion of the spool. This is presently a difficult task primarily because of the design of the restrictor, which is a metal stamping. The release of the nut strip also requires a special tool. In the fastener installation head of this invention, the restrictor comprises a metal part, preferably a cast metal part, pivotally supported on the nose member, having a finger which extends into the first nut bore of the first nut adjacent the plunger passage. The finger is biased by a spring into the nut bore. The second leg of the feed pawl also includes a projecting portion which may be easily gripped by the operator. The nut strip may thus be easily removed from the fastener installation head simply by depressing the nut restrictor and the second leg portion of the feed pawl, releasing the nut strip and permitting removal of the nut strip from the fastener installation head.